Upon infecting the host, mycobacteria trigger various responses from the cellular immune system. These responses originate with the antigen- presenting cell, which engulfs mycobacteria or their products and displays fragments of mycobacterial proteins in conjunction with the membrane proteins of the MHC. The macrophage is the primary APC for mycobacteria, but macrophages require "activation" in order to stimulate the immune system effectively. Unlike resting macrophages, activated macrophages express additional forms of MHC and/or stimuli for antigen- responding T cells which act outside the T cell receptor to provide costimulatory signals. Also, activated macrophages produce cytokines which provide additional signals to T cells. There is evidence that the immune response is determined at least in part by the combination of signals that macrophages provide to T cells. Several reports have indicated that different mycobacterial strains activate macrophages differently, and that these differences correlate with in vivo virulence as determined by the mycobacterial genome. Other reports have indicated that environmental factors, particularly oxygen tension, produce phenotypic changes in mycobacteria which alter their ability to stimulate the immune system and to cause disease. The nature of the mycobacterial components involved is still under investigation, but the 65-kD heat shock protein (hsp65) has received special attention. Consequently, this project will exam the hypothesis that the outcome of infection by M. tuberculosis is determined by the initial interactions between mycobacteria and macrophages. Virulent and avirulent strains of mycobacterial will be compared for their ability to induce macrophages to activate CD4+ helper T cells, CD4+ suppressor T cells, and CD4-8- alpha-beta and delta-gamma T cells, and for their ability to activate macrophages to express factors which are immunostimulatory (IL-1, TNF- alpha, IL-6, IL-8, and IL-12) or immunoinhibitory (TGF-beta and IL-10). Different culture conditions and oxygen environments will be used to bring out any phenotypic changes in mycobacteria which could affect their interactions with macrophages. Finally, using recombinant DNA techniques, the macrophage-activating domains of hsp65 and other mycobacterial proteins will be mapped. When these studies are complete, the knowledge gained may contribute to the design of more effective vaccines and immunotherapies for tuberculosis.